This invention relates to knitting machine parts. More particularly, this invention relates to knitting machine parts which have improved resistance to abrasion caused by knitting yarns of cut-resistant fiber.
Knitting needles used in automatic knitting machines constantly rub against the base of the needle bed during operation of the knitting machine, causing friction and a high occurrence of broken needles. To overcome this problem, knitting needles have been made with materials such as SK material (carbon tool steel), SKS material (alloy tool steel) and the like, which have been heat-treated to increase the abrasion resistance thereof.
However, a new problem has arisen in recent years due to the use of synthetic fibers in knitting yarns. Such fibers tend to increase the friction between the knitting needle and the yarn during the knitting process, resulting in abrasion to the knitting needle at the areas in which the needle comes into contact with the yarn.
To eliminate this problem, knitting needles have been made from sintered hard alloys having high abrasion resistance. However, the bend resistance of sintered hard alloys tends to decrease when the abrasion resistance thereof is increased.
Other efforts to improve the abrasion resistance of knitting needles have involved providing the knitting needle with an abrasion resistant coating. Knitting needles with such coatings are disclosed, for example, in Japanese Kokai Patent Application No. Sho 62[1987]-28452; Japanese Kokai Patent Application No. Sho 62[1987]-28453; Japanese Kokai Patent Application No. Sho 62[1987]-41358; Japanese Kokai Patent Application No. Hei 4[1992]-66659. In Japanese Kokai Patent Application No. Sho 62[1987]-28452 ("JP-28452"), a knitting needle is coated with a metal carbide, such as, e.g., titanium carbide. The titanium carbide coating may contain 7% by weight or less of oxygen, nitrogen, etc. The metal carbide coating can be made by a plasma chemical vapor deposition (CVD) process. JP-28452 teaches that, to form a titanium carbide coating, the base material temperature used during the plasma CVD process ranges from 400.degree. C. to 600.degree. C. JP-28452 further teaches that the metal carbide coating provides the knitting needle therein with high abrasion resistance in those portions of the needle which come into contact with the needle bed, the knitting yarn, and the drive unit.
Japanese Kokai Patent Application No. Sho 62[1987]-28453 ("JP-28453") teaches a knitting needle coated with a metal nitride, such as, e.g., titanium nitride. The titanium nitride coating may contain about 1% by weight or less of oxygen, carbon, and the like. The metal nitride coating may be made by reactive sputtering or by ion plating. During the reactive sputtering process, the base material temperature ranges from about 200.degree. C. to 300.degree. C. During the ion plating process, the base material temperature ranges from about 20.degree. C. to about 350.degree. C. In the example set forth in this reference, titanium nitride (sample A) is formed using a base material temperature of 300.degree. C. JP-28453 further teaches that the metal nitride coating provides the knitting needle therein with high abrasion resistance in those portions of the needle which slide on needle beds, contact the knitting yarn, and contact the drive unit.
In Japanese Kokai Patent Application No. Sho 62[1987]-41358 ("JP-41358"), a knitting needle is coated with a metal oxide material, e.g., titanium oxide. The metal oxide coating may be made by reactive sputtering or by ion plating. During the reactive sputtering process, the base material temperature ranges from about 200.degree. C. to 300.degree. C. During the ion plating process, the base material temperature ranges from about 20.degree. C. to about 350.degree. C. JP-41358 teaches that the metal oxide coating therein improves the abrasion resistance of those portions of the knitting needle that slide on needle beds, contact the knitting yarn and contact the drive unit.
In Japanese Kokai Patent Application No. Hei 4[1992]-66659 ("JP-66659"), objects such as cutter edges, sewing machine needles, and circular blades, are provided with a titanium nitride coating composed mainly of Ti.sub.2 N formed by a physical vapor deposition process. In distinguishing between Ti.sub.2 N and TiN, this reference states that the formation of TiN coatings by a CVD process requires high temperatures (800.degree. C. and higher), whereas Ti.sub.2 N coatings can be formed by a CVD process at temperatures ranging from as low as room temperature to 600.degree. C. JP-66659 does not disclose what items (e.g., needle beds, knitting yarn, etc.) the coated objects disclosed therein are resistant to.
Although the aforementioned JP-28452, JP-28453 and JP-41358 references each disclose that the coated knitting needles therein are resistant to, among other things, knitting yarns, none of these references teach whether the yarns are cut-resistant. The present invention is based in part on the discovery that yarns of cut-resistant fiber, particularly cut-resistant fiber that contains a hard particulate filler, are more abrasive to knitting machine parts than are conventional non-cut-resistant-fiber yarns. Thus, a particular coating on a knitting machine part which improves the part's resistance to abrasion caused by knitting conventional yarns may not provide the part with abrasion-resistance against yarns of cut-resistant fiber. For example, it has been found that titanium nitride coatings are not hard enough to resist CRF.RTM. yarn, where CRF yarn is comprised of polyester filaments that contain hard particles, such as alumina. (CRF is a registered trademark of HNA Holdings, Inc.). Thus, it is desirable to provide a coating for a knitting machine part which provides the knitting machine part with improved resistance to a yarn comprised of particle-filled cut-resistant fiber.
Chemical vapor deposition (CVD) has been used to form coatings on knitting machine parts. For example, the use of such a process is taught in JP-28452, which was mentioned hereinabove. In forming a coating layer on a knitting machine part by a CVD process, it is desirable that the processing temperature not be excessively high, e.g., greater than 1000.degree. C. Processing temperatures which are too high can cause excessive warping of the knitting machine part as well as compromise the shaping workability, hardness and breaking resistance of the part. For example, it has been found that although titanium carbide coatings and certain titanium carbonitride coatings containing low levels of nitrogen relative to carbon provide abrasion resistance to knitting machine parts, the high CVD temperatures involved in forming such coatings damage the parts. However, while excessively high CVD process temperatures are undesirable, it is at the same time desirable that the temperature of the CVD process be high enough to allow the coating to be strongly adhered to the part. Thus, it would be desirable to provide a coating for a knitting machine part which improves the resistance of the part to abrasion caused by knitting CRF yarn and which can be formed on the part by means of a CVD process which uses a deposition temperature that is too low to cause warpage of the part but high enough to provide a strong adherence between the coating and the knitting machine part.
Accordingly, a primary object of this invention is to provide a knitting machine part having improved resistance to abrasion caused by knitting a yarn comprising a particle-filled cut-resistant fiber.
A further object of this invention is to provide a knitting machine part having improved resistance to abrasion that is caused by knitting a yarn comprised of cut-resistant fiber, wherein such abrasion-resistance is provided to the part by a coating which can be formed on such part by a chemical vapor deposition process at a temperature which is low enough to avoid warping of the part but high enough to provide strong adherence between the coating and the part.
These and other objects which are achieved according to the present invention can be discerned from the following description.